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Ann Clin Nutr Metab 2023;15(2):51-56
Published online August 1, 2023
Changes in mineral and vitamin profiles after bariatric surgery in Korea: a before and after study
Jong Seob Park1,2, Sang-Moon Han1,3

1Department of Surgery, CHA Gangnam Medical Center, Seoul, Korea; 2Department of Surgery, Myongji Hospital, Goyang, Korea; 3Department of Surgery, Seoul Medical Center, Seoul, Korea
Correspondence to: Sang-Moon Han, email:
Received March 21, 2023; Revised June 22, 2023; Accepted June 27, 2023.
© 2023 The Korean Society of Surgical Metabolism and Nutrition and The Korean Society for Parenteral and Enteral Nutrition.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Purpose: Bariatric surgery induces nutritional deficiencies that require long-term monitoring and supplementation. This study aimed to evaluate the status of vitamins and minerals pre-operation and 2 years post-operation and to compare the findings according to type of bariatric surgery.
Methods: The study enrolled 302 patients who underwent bariatric surgery, adjustable gastric band (AGB), sleeve gastrectomy (SG), or Roux-en-Y gastric bypass (RYGB) between 2013 and 2017 in the CHA Gangnam Medical Center and the Seoul Medical Center, Korea. Minerals and vitamin status was assessed at baseline (pre-operatively) until 2 years after bariatric surgery.
Results: Mean age was 34.1±8.3 years, 256 patients (84.8%) were female, and mean body mass index was 35.3±5.7 kg/m2. Vitamin B1, vitamin B12, and folic acid levels were significantly different at 1 and 2 years after surgery compared to baseline. Hemoglobin, hematocrit, high-density lipoprotein, iron, calcium, and magnesium levels did not differ significantly during the study period.
Conclusion: Although enrolled patients had no clinical symptoms of nutritional deficiences, several indicators related to nutrition decreased at 2 years after bariatric surgery. Despite variations in the alteration of laboratory results across three surgical interventions, namely SG, AGB, and RYGB, a consistent reduction in fasting blood sugar was observed subsequent to the surgical procedures.
Keywords : Body mass index; Gastrectomy; Gastric bypass; Lipoproteins; Follow-up studies


Obesity is a major health concern worldwide. In 2016–2017, 4.7% of the Korean population met the criterion for obesity, with a body mass index (BMI) of 30 kg/m2 or higher, and 9.5% had comorbid diabetes mellitus. Other East Asian countries have reported 3.7%–8.2% of the population with a BMI of 30 kg/m2 or higher [1]. Improvements in eating habits can reduce body weight by 2%–6%, but after 1–5 years, 90% of patients are unable to maintain this weight loss and return to their original body weight or higher. Medication can also cause 5%–15% weight loss, but long-term results are poor, and side effects can occur [2,3]. Metabolic surgery for obesity has a far greater weight loss effect than do nonsurgical methods and aids in maintaining weight loss for a prolonged period after surgery [4]. Studies that have investigated the long-term effects of bariatric surgery have reported improvements in comorbid diseases such as type 2 diabetes, high blood pressure, and sleep apnea [5-7]. The results of a long-term randomized controlled trial for type 2 diabetes and cardiovascular disease showed that bariatric surgery had superior results to drug treatment [8]. However, postoperative or gastrointestinal complications can occur, and various symptoms such as anemia, bone metabolism, vitamin deficiency, mineral deficiency, and protein malnutrition that require continuous supplementation may develop over time [9,10]. The American Clinical Endocrine Society, Obesity Society, and Obesity Metabolism Society have published guidelines for vitamin and mineral intake after bariatric surgery [11-13]. However, eating habits and food culture in Korea differ from those in the United States, and it is questionable whether the USA guidelines will provide sufficient vitamin and mineral supplementation in Koreans.


Purpose of this study is to evaluate of nutritional status of patient before and after the bariatric surgery. Specifically change of followings were measured; body weight, BMI, fasting blood sugar, HbA1c, total cholesterol, low-density lipoprotein, high-density lipoprotein, triglyceride, vitamin B1, vitamin B12, iron, calcium, magnesium, folic acid, hemoglobin, and hematocrit. The change according to 3 procedures were also compared, inclduding the sleeve gastrectomy (SG), adjustable gastric banding (AGB), and Roux-en-Y gastric bypass (RYGB).


Ethics statement

This study was approved by the CHA Gangnam Medical Center Institutional Review Board (approval number: GCI-18-32). The obtainment of informed consent was exempted by the Institutional Review Board.

Study design

It is a before and after study. A retrospective analysis of a prospectively collected database was done. It was described according to TREND statement (


This study was conducted at 2 hospitals, including the CHA Gangnam Medical Center and the Seoul Medical Center, Korea between January 2013 and December 2017. After recruiting patients who underwent bariatric surgery, the following data were collected and analyzed before and after the surgery: laboratory-determined mineral and vitamin levels in addition to age, sex, weight, BMI, and medical history. Data chosen to evaluate nutritional status included hemoglobin, hematocrit, fasting blood sugar, HbA1c, total cholesterol, high-density lipoprotein, low-density lipoprotein, triglycerides, iron, calcium, vitamin B1, vitamin B12, folic acid, and magnesium. All patients who underwent bariatric surgery were instructed to take multivitamin tablets. Indications for bariatric surgery were as follows: BMI ≥35 kg/m2 or BMI ≥30 kg/m2 with comorbidities such as hypertension, dyslipidemia, type 2 diabetes, obstructive sleep apnea, or other comorbidities related to morbid obesity.


Patients who underwent bariatric surgery and were monitored for more than 1 year were enrolled in this study. Patients lost to follow-up within 1 year or those who had insufficient laboratory data were excluded. Finally, 302 patients were included as participants.


Surgical intervention was the bariatric surgery, including SG, AGB, and RYGB. Patients underwent one of 3 procedures. SG was considered for most morbidly obese patients. AGB was considered for patients who were relatively low BMI without comorbidities, while RYGB was performed in patients with high BMI and severe DM as well as other comorbidities after consultation with the patient.


Weight, BMI, and all laboratory values are outcomes.

Data sources/measurement

Electronic medical records of the partcipants in 2 hospitals were data analyzed. Outcome values of collected and tabulated.


There was no selection bias since all target population was included.

Study size

All target population was included in the analysis so that sample size estimation was not done. Posthoc analysis of matched pair by G*Power ver. (Heinrich Heine Universität Düsseldorf; showed that the power is 1.0 when the effect size is set to 0.5, alpha error probability 0.05 and sample size 302.

Assignment method

No special assignment was necessary.

Blinding (masking)

No blinding was done.

Unit of analysis

The unit of analysis was the same group (before and after).

Statistical methods

Data were analyzed using descriptive statistical methods via the SPSS for Windows (version 26.0; IBM Corp.). These data are presented as either mean±standard deviations or percentages. Paired t-test, repeated measures ANOVA, Friedman’s test, and Wilcoxon signed rank test were used to compare general and serum laboratory values before and after surgery. Data were evaluated using Kolmogorov–Smirnov and Shapiro–Wilk tests. A P-value less than 0.05 was considered statistically significant.



Average age was 34.1±8.3 years. Among a total of 302 patients, 256 (84.8%) were female. Average weight was 96.1±19.3 kg and average height was 164.6±7.7 cm. Fatty liver disease was present in 132 (43.7%), dyslipidemia in 130 (43.0%), hypertension in 114 (37.7%), hiatal hernia in 98 (32.5%), diabetes in 67 (22.2%), insulin resistance in 66 (21.9%), obstructive sleep apnea in 46 (15.2%), and reflux esophagitis in 42 patients (15.2%). SG was performed in 271 (89.7%), AGB in 19 (6.3%), and RYGB in 12 patients (4.0%; Table 1).

General patient characteristics

Characteristics Value (n=302)
Age (yr) 34.1±8.3
Female 256 (84.8)
Male 46 (15.2)
Weight (kg) 96.1±19.3
Height (cm) 164.6±7.7
Body mass index (kg/m2) 35.3±5.7
Fatty liver 132 (43.7)
Dyslipidemia 130 (43.0)
Hypertension 114 (37.7)
Hiatal hernia 98 (32.5)
Diabetes mellitus 67 (22.2)
Insulin resistance 66 (21.9)
Obstructive sleep apnea 46 (15.2)
Reflux esophagitis 42 (13.9)
Arthritis & back pain 34 (11.3)
Gout 21 (7.0)
Gallbladder stones 19 (6.3)
Asthma 12 (4.0)
Major depressive disorder 9 (3.0)
Arrhythmia 3 (1.0)
Type of bariatric surgery
Sleeve gastrectomy 271 (89.7)
Adjustable gastric banding 19 (6.3)
Roux-en-Y gastric bypass 12 (4.0)

Values are presented as mean±standard deviation or number (%).

Main results

Weight and BMI

Average weight before surgery was 96.1±19.3 kg; after 1 and 2 years, average weight was 64.2±11.5 kg (33.2% decrease) and 67.8±13.5 kg (29.4% decrease) (P<0.001), respectively. BMI decreased from 35.3±5.7 kg/m2 before surgery to 18.2±10.3 kg/m2 at 1 year and 18.8±11.7 kg/m2 at 2 years after the operation (P<0.001; Table 2).

Changes in weight and body mass index postoperatively

Baseline (pre-operatively) 6 months 1 year 2 years P-value
Weight (kg) 96.1±19.3 70.0±13.3 64.2±11.5 67.8±13.5 <0.001***
Body mass index (kg/m2) 35.3±5.7 22.1±9.7 18.2±10.3 18.8±11.7 <0.001***

Values are presented as mean±standard deviation.


Laboratory findings

Fasting blood sugar, HbA1c, total cholesterol, low-density lipoprotein, triglyceride, vitamin B1, vitamin B12, and folic acid levels decreased significantly from preoperative levels to 1 and 2 years after surgery. Hemoglobin, hematocrit, high-density lipoprotein, iron, calcium, and magnesium levels did not differ significantly during the study period (Table 3).

Changes in serum laboratory values

Preoperation 1 year 2 years P-value
Hemoglobin (×103/μL) 14.1±1.5 13.3±1.3 13.2±1.7 0.159
Hematocrit (%) 40.8±3.5 39.1±3.3 38.9±4.3 0.478
Fasting blood sugar (mg/dL) 110.3±29.7 93.7±14.0 94.8±8.7 <0.001***
HbA1c (%) 6.2±1.3 5.5±0.5 5.5±0.4 <0.001***
Total cholesterol (mg/dL) 202.2±36.5 185.9±30.1 182.7±24.4 0.008**
High-density lipoprotein (mg/dL) 50.5±12.7 62.3±13.9 60.8±13.9 0.127
Low-density lipoprotein (mg/dL) 128.0±34.4 105.6±28.2 103.6±25.4 <0.001***
Triglycerides (mg/dL) 148.6±84.1 87.9±41.3 89.2±41.4 <0.001***
Iron (mcg/dL) 99.4±40.4 100.0±36.0 101.4±42.8 0.903
Calcium (mg/dL) 9.2±0.4 9.2±0.4 9.2±0.4 0.157
Vitamin B1 (ng/mL) 147.4±29.4 127.8±28.8 126.3±25.9 0.003**
Vitamin B12 (ng/mL) 547.5±198.5 468.9±175.4 516.4±251.7 <0.001***
Folic acid (ng/mL) 8.9±4.7 10.3±6.7 8.8±4.4 0.001**
Magnesium (mg/dL) 2.3±0.3 2.3±0.3 2.3±0.4 0.335

Values are presented as mean±standard deviation.

**P<0.01, ***P<0.001.

Comparison according to surgical procedures

In the SG group, there were significant differences in fasting blood sugar, HbA1c, triglyceride, and vitamin B12 levels from baseline. In patients who underwent AGB, fasting blood sugar, low-density lipoprotein, triglyceride, iron, vitamins B1, B12, folic acid, and magnesium levels decreased significantly from baseline. In the RYGB group, fasting blood sugar, HbA1c, triglyceride, and folic acid levels were significantly different post-surgery compared to baseline (Table 4).

Changes in serum laboratory values according to time after surgery

Sleeve gastrectomy Adjustable gastric banding Roux-en-Y gastric bypass

Preoperation 1 year 2 years P-value Preoperation 1 year 2 years P-value Preoperation 1 year 2 years P-value
Hemoglobin (×103/μL) 14.1±1.3 13.3±1.3 12.9±1.9 0.101 14.2±1.6 13.0±1.2 13.6±1.4 0.091 14.2±2.0 13.8±1.4 13.4±0.8 0.381
Hematocrit (%) 41.2±3.3 39.0±3.2 38.5±4.8 0.522 41.1±3.8 38.2±3.7 39.6±3.7 0.220 41.0±4.5 39.7±3.2 38.8±3.2 0.658
Fasting blood sugar (mg/dL) 111.9±39.5 91.8±14.2 92.0±7.9 <0.001*** 99.0±16.1 96.8±12.3 95.6±7.4 0.004** 134.6±45.7 102.7±10.2 102.6±8.6 <0.001***
HbA1c (%) 6.2±1.4 5.4±0.4 5.3±0.3 <0.001*** 5.7±0.5 5.6±0.4 5.3±0.3 0.458 8.0±2.1 5.9±0.5 5.7±0.3 <0.001***
Total cholesterol (mg/dL) 200.8±37.7 188.5±32.0 182.9±27.6 0.068 196.8±33.0 180.7±21.3 188.8±19.1 0.106 182.1±41.7 171.6±29.8 175.1±24.4 0.072
High-density lipoprotein (mg/dL) 51.4±13.4 65.2±13.5 67.8±13.2 0.422 49.8±10.7 53.5±11.9 52.6±8.4 0.408 50.9±12.0 50.8±8.4 52.6±11.2 0.536
Low-density lipoprotein (mg/dL) 127.2±38.2 104.2±29.2 99.3±25.0 0.042* 120.4±26.7 110.6±23.3 115.0±21.1 0.002** 108.2±39.0 104.9±30.1 98.5±30.5 0.447
Triglycerides (mg/dL) 151.7±103.3 80.0±35.8 73.9±30.4 0.001** 129.1±64.7 108.5±54.8 109.2±54.8 0.012* 149.7±81.8 115.9±36.2 112.3±35.8 0.004**
Iron (mcg/dL) 97.5±42.1 102.9±37.6 103.0±52.9 0.362 111.8±43.5 96.4±33.3 98.6±26.4 <0.001*** 81.8±25.7 87.6±25.3 95.7±32.0 0.260
Calcium (mg/dL) 9.2±0.4 9.2±0.4 9.2±0.4 0.088 9.2±0.3 9.2±0.3 9.3±0.3 0.757 9.2±0.4 9.3±0.2 9.2±0.2 0.088
Vitamin B1 (ng/mL) 146.3±36.3 127.0±40.9 124.6±23.9 0.270 149.1±17.1 133.6±24.3 126.4±27.7 0.022* 150.8±38.6 141.2±22.7 135.4±27.2 0.096
Vitamin B12 (ng/mL) 576.3±402.0 459.5±179.2 515.7±154.9 <0.001*** 551.1±239.2 527.7±175.3 523.9±178.7 0.009** 583.5±158.5 500.4±153.3 502.7±145.9 0.130
Folic acid (ng/mL) 8.0±4.5 10.2±7.3 8.5±3.8 0.169 8.7±3.9 8.2±3.8 7.6±3.5 0.001** 10.6±4.9 11.5±5.1 11.6±6.0 0.038*
Magnesium (mg/dL) 2.2±0.3 2.2±0.3 2.2±0.2 0.438 2.5±0.3 2.4±0.4 2.5±0.6 <0.001*** 2.0±0.1 2.3±0.3 2.2±0.1 0.061

Values are presented as mean±standard deviation.

*P<0.05, **P<0.01, ***P<0.001.


Interpretation/comparison with previous studies

Indicators of diabetes or hyperlipidemia improved after bariatric surgery. Vitamin B1, vitamin B12, and folic acid levels were significantly different at 1 and 2 years after surgery compared to baseline. These results are consistent with those of other studies conducted over a similar period [14].

Iron deficiency is the main cause of anemia after bariatric metabolic surgery; a secondary cause is vitamin B12 deficiency. Hemoglobin and iron levels showed no significant differences preoperatively and at the 2-year follow-up. However, vitamin B12 level showed a statistically significant decrease from baseline at the 2-year follow-up. Iron deficiency in SG and RYGB patients reportedly occurs in 30%–50% of patients 5 years after surgery [15,16]. One meta-analysis found that SG and RYGB are comparable with regard to the risk of postoperative anemia and iron deficiency [17]. Since the risk of iron deficiency is high regardless of the type of bariatric surgery, close follow-up and multivitamin and trace element supplementation are required. Active iron supplementation is necessary for patients with iron deficiency.

Vitamin B12 deficiency has also been reported in 19%–35% of bariatric surgery patients after 5 years [18]. Therefore, one study recommended vitamin B12 supplementation as follows: systematic vitamin B12 supplementation administered orally at a daily dose of 250–350 g/day or a weekly dose of one or two 1,000 g-vials of vitamin B12 [19]. In this study, vitamin B12 and folic acid levels decreased at 1 year after surgery but increased slightly at 2 years. The reason for this is unclear, but it may be related to the slight increase in weight in the second year after surgery compared to the first year and an increase in the amounts of vitamins and minerals ingested during this period. We found vitamin B12 deficiency in those patients who had undergone SG but not in those who had undergone RYGB. Several papers have suggested that RYGB surgery is associated with a higher risk of vitamin B12 deficiency than is SG surgery [15,20,21]. This difference may result from the more favorable effect of SG on the metabolism of vitamin B12 than of RYGB as it results in lower malabsorption than RYGB [20]. In one study, vitamin B12 status at 1 year showed no difference between SG and RYGB groups, but at 4 years, the RYGB group showed vitamin deficiency [15]. The discrepancy between our findings and those of previous studies are likely related to sample size and differences in study periods.

Vitamin B1 and magnesium deficiencies are associated with Gayet-Wernicke syndrome. Vitamin B1 level was significantly lower after surgery than before surgery, but magnesium level was not significantly different pre- and postoperatively. None of the patients in our study had symptoms related to Gayet-Wernicke syndrome. One study reported a 6% vitamin B1 deficiency in 2 years and stated that vitamin B1 administration is necessary for patients who have frequent digestive disorders such as vomiting [19,22]. According to a review article, however, vitamin B1 deficiency in both SG and AGB was showed but, has not consistently been reported in patients undergoing RYGB [23].


Several limitations of our study should be noted. It was retrospective in design and the follow-up period was short. Since many studies have reported nutritional and mineral deficiencies 3–5 years after surgery, continuous monitoring and future research with additional follow-up assessments are needed. In addition, vitamins A, D, E, and K levels were not determined, nor were levels of trace elements such as zinc and copper. After bariatric surgery, patients were instructed to take multivitamins; however, the type or dosage was not specified, and compliance with multivitamin intake was not assessed. One study suggested that many patients who undergo bariatric surgery do not receive the recommended nutritional monitoring after discharge [16]. Therefore, close nutritional monitoring is necessary when patients visit the clinic for follow-up. If this limitation is resolved in the future, it will greatly help educate patients on vitamin intake after bariatric surgery. Future long-term studies are required to further investigate the long-term effects of bariatric surgery on nutritional status.


Several indicators related to nutrition decreased 2 years after bariatric surgery despite the absence of clinical symptoms in the patients enrolled in this study. Although there was a difference of change of laboratory findings according to 3 surgical procedures, including SG, AGB, and RYGB, fasting blood sugar decreased after the surgery consistently. Above results also may be able to contribute to the basic data for providing the guidelines on the vitamin and mineral intake after bariatric surgery for patients in Korea.

Authors’ contribution

Conceptualization: JSP, SMH. Data curation: SMH. Formal analysis: JSP. Funding acquisition: JSP. Investigation: JSP, SMH. Methodology: JSP. Project administration: JSP. Resources: SMH. Software: JSP. Supervision: SMH. Validation: SMH. Visualization: JSP. Writing – original draft: JSP. Writing – review & editing: all authors.

Conflict of interest

The authors of this manuscript have no conflicts of interest to disclose.


The authors received financial support from the Korean Society of Surgical Metabolism and Nutrition.

Data availability

Contact the corresponding author for data availability.



Supplementary materials


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